This study is designed to look at the safety of SB-207266-A in the treatment of Irritable Bowel Syndrome (IBS) over a further 36 week period. All patients who took part in Study 051 will be offered the chance to take part in the new study. This new medication has already been given to approximately 300 patients with IBS and 136 healthy volunteers. Most of these subjects have been treated for 12 weeks, although some subjects have now been treated for up to 12 months. The next step is to assess this new medication in larger numbers of subjects over longer periods of time.